ST72344K2 datasheet(138/247 Pages) STMICROELECTRONICS

138 / 247 page

On-chip peripherals

ST72344xx, ST2345xx

138/247

Doc ID 12321 Rev 6

Conventional baud rate generation

The baud rates for the receiver and transmitter (Rx and Tx) are set independently and

calculated as follows:

with:

PR = 1, 3, 4 or 13 (see SCP[1:0] bits)

TR = 1, 2, 4, 8, 16, 32, 64,128

(see SCT[2:0] bits)

RR = 1, 2, 4, 8, 16, 32, 64,128

(see SCR[2:0] bits)

All these bits are in the SCIBRR register.

Example: If fCPU is 8 MHz (normal mode) and if PR = 13 and TR = RR = 1, the transmit and

receive baud rates are 38400 baud.

Note:

The baud rate registers MUST NOT be changed while the transmitter or the receiver is

enabled.

Extended baud rate generation

The extended prescaler option gives a very fine tuning on the baud rate, using a 255 value

prescaler, whereas the conventional Baud Rate Generator retains industry standard

software compatibility.

The extended baud rate generator block diagram is shown in Figure 65.

The output clock rate sent to the transmitter or to the receiver is the output from the 16

divider divided by a factor ranging from 1 to 255 set in the SCIERPR or the SCIETPR

Note:

The extended prescaler is activated by setting the SCIETPR or SCIERPR register to a value

other than zero. The baud rates are calculated as follows:

with:

ETPR = 1, ..., 255 (see SCIETPR register)

ERPR = 1, ..., 255 (see SCIERPR register)

Receiver muting and wakeup feature

In multiprocessor configurations, it is often desirable that only the intended message

recipient should actively receive the full message contents, thus reducing redundant SCI

service overhead for all non addressed receivers.

The non-addressed devices may be placed in sleep mode by means of the muting function.

Tx =

(16*PR)*TR

fCPU

Rx =

(16*PR)*RR

fCPU

Tx =

16*ETPR*(PR*TR)

fCPU

Rx =

16*ERPR*(PR*RR)

fCPU

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